Many industrial limit switches utilize return springs in their operator heads to effect return of the operating shafts and machine element engaging arms to a center or non switch operating positions following disengagement from a moving machine element. Such return springs store energy as a result of rotation of their associated operating shafts. If the operating arms on such shafts are suddenly released by a moving machine element the stored energy in the return springs can, under certain conditions, cause the operating shaft to reversely rotate back to and beyond its center position. Such reverse rotation beyond center position can result in unwanted switch commutations, particularly when the degree of shaft rotation required for switch commutation is small.
The Duncan et al U.S. Pat. No. 3,793,492 discloses an improved Limit Switch Operating mechanism wherein by selectable adjustment of a member within an operating head subassembly switch commutations can be made to occur in either or both directions of operator shaft rotation. Upon release of the arm fixed on the shaft by a moving machine part or the like, a helically coiled torsion spring in the operating head subassembly acts to effect snap-back return of the operator shaft to a center position from either direction or rotation. As commutations of the contacts in that limit switch can be set to occur at as little as 5.degree. of operator shaft rotation, it is desirable to prevent telegraphing oscillations of the operator shaft through and beyond its center position that could occur under the conditions aforementioned.